This section describes the optical components of the UHRF. This overview is intended for AAT support staff but may be of interest to visiting astronomers.
- Coude Projection Factors
- The Pre-Slit Room
- The Coude East Room
- The Coude East Ante Room
- The UCLES/UHRF Engineering GUI
The fluorescent lights for the pre-slit room are controlled from the covered switch on the outside wall, located near the entrance hatch.
Calibration lamps and filter slit wheel
The ThAr arc lamp for UHRF is located on the engineered track (which replaces the infamous Lego track) which allows it to illuminate the slicer directly. If the arcs seem unusually faint, have the night assistant check the alignment of this lamp as it may have been bumped (e.g. after a SemelPol run). The UHRF HeNe laser and diffuser disk is in the large black box on the telescope side of the slit head. This box also contains a quartz lamp. Lift the cover on the side of this box to see the lamps. The UHRF lamp wheels are also in this box. The quartz lamp used by UHRF is mounted on the LF2 filter wheel at position 8.
The TV camera has two positions: on top for UCLES and for UHRF+slit, or front on (near the UHRF ThAr lamp) for UHRF+image slicer. For UHRF, ensure that the Beam Rotator is OUT, or it will hit the TV!
In most cases UHRF is used with an image slicer which cuts the image into slices of width 30 microns. In general, use the slicer for all frames except flat fields. The entrance is a 'pin-hole' of size 20 mm (about 1.5 arcsec). The back plate of the slicer is stopped down with two L-shaped pieces. This is held in place with three springs - these may occasionally need to be clicked back in place. The drive between slit and slicer positions can be a bit jerky. The slicer cuts an order into about 35 slices, which are masked down to around 24 slices.
For flat fields, use a long and wide slit for flat fields to see pixel-pixel variations. Flats should also be taken through the slicer to see the geometric properties of the slicer itself.
UHRF can also be used with the slit instead of the slicer although this is rarely done. The slit mode is only used with the detector at the 3E5 position. A slit width of approximately 0.6 arcsec then gives a degraded resolution of about 1E5. Note that the UHRF ThAr lamp is not on the same axis for the slit and slicer, and needs to be aligned manually for use with the slit. This mode has been used to improve the throughput on faint objects. However in most cases it is advisable to use UCLES for objects fainter than around 13th magnitude.
The Focal Modifier is always used with UHRF and is brought into the beam during the configuration process. The UHRF focal modifier is the short one. There are also two UCLES modifiers in the pre-slit room, these are longer and thinner.
Filters are used in UHRF as follows:
- For blue wavelengths it is advisable to use a bandpass filter to cut out scattered red light. Examples are UG11 centred at 3300 Å and BG12 centred at 4000 Å. Note that this gives some loss in transmission - and the blue filters have strong red leaks. The two filter wheels are aligned on the same optical axis - set one to the clear position and the other to the filter position.
- For red wavelengths it works well to use a `cut-on' filter such as RG630 to cut out scattered blue light and to avoid order overlap. These have a sharp cut-off profile at the low wavelength edge.
- As described in the UHRF setup procedures, a filter is also used in front of the TV lens to correct for atmospheric dispersion.
- The Schott Coloured Glass catalogue of filters is available in the library.
The slit shutter is located in the wall between the pre-slit room and coude room. It is controlled from the ODC, provided the cable is connected to the CCD controller.
Collimator + EchelleThe UHRF collimator + echelle unit slides into place when UHRF is configured, and should slide out of the way for UCLES. Be aware that the lower Hartmann barn door has been known to fall off!
Secondary CollimatorThe focus of this is set by a ray trace model of the spectrograph and is not absolutely correct.
Cross Dispersers and Camera LensU, B, V and R cross-dispersers are available. There are also two mirrors called MB and MR which can be used to give the full spectrum.
Focal Reducers and CCDTwo different focal reducing lenses are used to give the 3E5 and 6E5 resolutions. Both lenses move aside for 1E6 resolution. These are located on a rotating table at the ends of the baffles used with the CCD.
Camera ShutterThe camera shutter is mounted front of the detector and is controlled by a switch on the panel in the coude ante-room and by microswitches on doors to the coude room and pre-slit room. If all your arcs and flats come out looking like biases, then suspect the camera shutter! Check the status lights on the "panic" button box in the control room (there should be at least one flashing red light - all green is bad!), and if necessary re-open the camera shutter by holding down the orange OPEN button on the panel in the ante-room until it lights.
Instrumental ResolutionThe detector can be placed at three different positions to give resolutions of approximately 3E5, 6E5 and 1E6. To change the detector position, remove the black baffles, check cables are out of the way, drive CCD to new position and reset the baffles. This procedure is normally done by the afternoon staff.
Syntel MicrocomputerThe Syntel Micro-computer takes commands from the Linux GUI and communicates with UHRF/UCLES. The Syntel terminal is located in the Coude East ante room. If the Syntel is hung up, try a couple of Cntrl-C's in quick succession. For a list of Syntel commands see the Appendix C8 of the Coude spectrographs manual.
Spectrograph Rack and Power SuppliesTo power down the spectrograph power supplies and shutter overides for UHRF and UCLES, turn off the switches labelled 5 4 3 2 1 in order, and power then up in the order 1 2 3 4 5.
> $UMIT_DEV/egui &
which will launch a new GUI. Click on the "Commands" tab, and select from the list of components on the left hand side. Enter a new numerical value, or select from the pull-down list of values (the lists are defined in the file $UMIT_DEV/../echelle.actions). Click on "Execute", and the command will be relayed to the Syntel microcomputer.
For example, to turn on the UCLES ThAr lamp while using the UHRF GUI, you can use the Engineering interface in order to select LAMP=THAR, TV_MIRROR=Wide field/Arc, and LAMP_ON=THAR. To turn it off again, select LAMP_ON=NONE, TV_MIRROR=Slit Viewing, and LAMP=NONE.
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Stuart Ryder, sdr -@- aao.gov.au